Wireless mobile networks, in which a User Equipment (UE), such as a mobile handset, communicates via a radio link to a network of base stations or other wireless access points connected to a telecommunications network, have recently undergone rapid development through a number of successive generations. The initial deployment of systems using analog signaling has been superseded by second Generation (2G) digital systems such as Global System for Mobile communications (GSM), which typically use a radio access technology known as GSM Enhanced Data rates for GSM Evolution Radio Access (GERA), combined with an improved core network.
The second generation systems have themselves been replaced by or augmented by third Generation (3G) digital systems such as Universal Mobile Telecommunications System (UMTS), using the Universal Terrestrial Radio Access (UTRA) radio access technology and a similar core network to GSM. Third generation standards provide for a greater throughput of data than is provided by second generation systems, and this trend is continuing in view of the proposals by the Third Generation Partnership Project (3GPP) of a new 4G system known as the Evolved Packet System (EPS), but which is more commonly referred to as the Long Term Evolution (LTE) system. LTE systems use an improved radio access technology known as Evolved UTRA (E-UTRA), which offers potentially greater capacity and additional features when compared with the previous standards, combined with an improved core network technology referred to as the Evolved Packet Core (EPC).
As in earlier wireless mobile standards, LTE is designed as a cellular system in which base stations, known as eNBs, provide coverage over one or more cells. In general, a mobile terminal in LTE, known as the User Equipment (UE), communicates with one base station and one cell at a time. The mobile terminal can exist in one of two communication states in LTE: an IDLE state in which the mobile terminal is basically on standby, and a CONNECTED state in which the mobile terminal has an active radio link to the base station.
In the IDLE state in LTE, the mobile terminal is tracked by the network to a specific tracking area, which may cover several base stations. The mobile terminal is not assigned to any particular base station, but may itself choose which base station or base stations it listens to. The main aim in this state is to minimize signaling and the consumption of resources, and thereby maximize standby time for terminals with limited battery power.
In contrast, in the CONNECTED state in LTE, the mobile terminal has a serving base station allocated to it, has its location tracked to the serving base station, and has active bearers which allow the terminal to transmit and receive at relatively high data rates.
If a failure occurs in the CONNECTED state, the terminal can lose its allocation to a serving base station. In this situation, there is a risk that the terminal may revert to the IDLE state along with an associated disruption to the data connections, including potential data loss. This disruption of the connection to the serving base station may be the result of a Radio Link Failure (RLF).
In an attempt to prevent the transition to an IDLE state, the UE may try to perform a connection re-establishment. If the connection re-establishment succeeds, the UE remains in CONNECTED and data loss may be prevented.
In the current LTE system, a User Equipment (UE) experiencing a Radio Link Failure (RLF) may have to execute certain steps before being able to access a cell in order tore-establish a connection. These steps may include performing a cell search and reading required system information.
Therefore, a need exists for a method and apparatus for preparing a mobile terminal for a possible radio link failure.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.